Optical fiber has become a widely accepted form of transmission media. A continuous length of the fiber is drawn from an optical preform which may be made by any one of several known processes. Afterwards, or as part of a tandem process, the drawn fiber is coated, cured, measured and taken up, desirably in an automatic takeup apparatus, on a spool. Methods and apparatus for taking up optical fiber are disclosed and claimed in U.S. Pat. No. 4,291,841 which issued on Sept. 29, 1981 in the names of P. W. Dalrymple, M. J. Hyle, D. L. Myers and J. W. Wright.
The spool on which the optical fiber is taken up has other uses. It is used to store the optical fiber, to pay out and to take up the fiber for other operations such as ribboning, cabling, and rewinding and is used to ship optical fiber which is wound thereon to other companies which further process the fiber.
It has been common practice in the industry to use a molded spool having disc-like flanges connected through a cylindrical hub and being molded from an ABS or polyethylene material, for example. Typically, the spool most commonly used to date includes a hub having a 10.2 cm traverse and a diameter of about 15.2 cm whereas the flange has a diameter of about 20.3 cm. Generally, the barrel or hub has been covered with a foam-like material which acts as a cushion and stabilizes the convolutions of the optical fiber.
The above-described spool proved to be quite satisfactory in the early years of optical fiber manufacture when the preform size limited the amount of fiber drawn from the preform and usually did not exceed about 2000 meters. Further, for these lengths, the winding pattern did not prove to be critical. In one pattern, the convolutions were such that the package had a greater diameter at a midpoint of the hub with a diameter which decreased gradually toward each flange. Another pattern included a package which was uniformly thick over most of the hub length and which had a tapered end adjacent to one of the flanges. See for example, U.S. Pat. No. 4,545,542 which issued on Oct. 8, 1985 in the names of R. E. Frazee, Jr. et al.
As one might expect, efforts were made to increase the size of the preforms to increase the length of the optical fiber in each draw run. In order to accomodate these longer runs, some optical fiber producers began to use a spool having a longer hub length, which improved the stability of the package by minimizing layer height build-up with a winding pattern which sloped downward toward the hub at one or both flanges. However, minimizing layer height and sloping the winding pattern resulted in a package which was smaller than the capacity of this spool. Another method included using a spool having larger diameter flanges than those used in the past and the winding of the optical fiber flange-to-flange. Winding flange-to-flange when the flanges are disc-like often times results in a gap being formed between the last convolution in a layer and the adjacent spool flange. As a result, the last convolution of the next successive layer may fall into the gap, may descend several layers and may cause a snarling during payout. In order to avoid this, an open wind pattern frequently is used, but this winding arrangement tends to reduce the capacity of the package.
A spool which is used in the takeup of optical fiber as well as for further processing and for shipping must also have at least one additional feature. Both ends of the optical fiber which is wound on the spool must be accessible for measurement and characterization purposes. It should be apparent that the last portion of the length of optical fiber which is wound on the spool is readily accessible. However, provisions must be made for accessing the initial portion of the length of the optical fiber which is wound on the spool. Also, following the measurement and characterization, it still may be desirable to have both ends accessible for further processing.
Such a sought after spool does not appear to be available in the prior art. What is needed and seemingly what is not provided is a spool on which a relatively long length of optical fiber may be taken up and which provides access to each end of the optical fiber. Further, the sought-after spool should be such that the package of optical fiber which is wound thereon is stable and is devoid of snarled convolutions which would impair payout of the optical fiber from the spool.